The present invention relates to a color picture tube device configured to obtain a high resolution across a whole screen of a picture tube. More specifically, the present invention relates to an electron gun used in the color picture tube device.
A color picture tube is required to have a high resolution. FIG. 8 shows an example of a conventional electron gun providing a high resolution color picture tube with a reliable and simple configuration, which is disclosed in JP 07(1995) 6706. As shown in FIG. 8, an electron gun 100 has cathodes 101, a control electrode 102, an accelerating electrode 103, a G3 electrode 104, a first focusing electrode 105, a second focusing electrode 106, a final accelerating electrode 107 and a shield cup 108, which are arranged in this order. The accelerating electrode 103 and the G3 electrode 104 form a prefocus lens, while the second focusing electrode 106 and the final accelerating 107 form a main lens.
A constant voltage Vg3 (9.0 kV) is applied to the G3 electrode 104, while a constant voltage Vfoc2 (6.5 kV) and a dynamic voltage Vd superimposed thereon are applied to the second focusing electrode 106, thereby keeping a relationship of Vg3 greater than Vfoc2.
The dynamic voltage, which is 0V when the deflection angle of an electron beam is 0, will rise gradually with the increase of the deflection angle. This strengthens a quadrupole lens electric field formed by the first focusing electrode 105 and the second focusing electrode 106.
In this configuration, the voltage Vg3 at the prefocus lens side can be applied separately from the voltage Vfoc2 configuring a main lens at the low voltage side. Thereby, the voltage Vfoc2 can be set lower than Vg3 while maintaining the level of the voltage Vg3. In this manner, the characteristics of the prefocus lens are maintained and a reliable color picture tube device having a high resolution can be provided.
In such a conventional electron gun, a sufficient potential difference is maintained between the voltage Vg3 (9.0 kV) and a voltage of the accelerating electrode 103, as the voltage of the accelerating electrode 103 is equal to the voltage Vfoc1 (600 V) applied to the first focusing electrode 105. However, a potential difference between the first focusing electrode 105 (600 V) and the second focusing electrode 106 (6.5 kV) is increased, causing the formation of a considerably strong quadrupole lens when an electron beam is not deflected. As a result, the quadrupole lens will have an increased astigmatism, limiting a reduction of the spot diameter of the electron beam on the screen.
Moreover in this configuration, Vfoc1 is lower than Vfoc2 under a non-deflection condition, and the dynamic voltage Vd is raised gradually with the increase in the deflection angle so as to change the quadrupole lens, and thus the sensitivity in correcting the deflection astigmatism with respect to the dynamic voltage is inferior.
In order to solve the above-described problems in conventional techniques, an object of the present invention is to provide a color picture tube device with a small beam spot diameter to provide a high resolution.
For achieving the above-described object, a first color picture tube device according to the present invention has an electron gun including cathodes, a control electrode, an accelerating electrode, a G3 electrode, a first focusing electrode, a second focusing electrode and a final accelerating electrode that are arranged in this order. A voltage applied to the G3 electrode is obtained by dividing with a resistor a voltage applied to the final accelerating electrode, and a relationship represented as Va greater than Vg3 greater than Vfoc2 is satisfied when an electron beam is not deflected, where Va denotes the voltage applied to the final accelerating electrode, Vg3 denotes the voltage applied to the G3 electrode, and Vfoc2 denotes a voltage applied to the second focusing electrode.
A second color picture tube device according to the present invention has an electron gun including cathodes, a control electrode, an accelerating electrode, a G3 electrode, a first focusing electrode, a second focusing electrode and a final accelerating electrode that are arranged in this order. A voltage applied to the G3 electrode is obtained by dividing with a resistor a voltage applied to the final accelerating electrode, a relationship represented as Vg3 greater than 9 kV is satisfied, and a relationship represented as Va greater than Vg3 greater than Vfoc1 greater than Vfoc2 is satisfied when an electron beam is not deflected, where Va denotes the voltage applied to the final accelerating electrode, Vg3 is a voltage applied to the G3 electrode, Vfoc1 denotes a voltage applied to the first focusing electrode and Vfoc2 denotes a voltage applied to the second focusing electrode.